Merge branch 'cw/worktree-extension'

Introduce a new repository extension to prevent older Git versions
from mis-interpreting worktrees created with relative paths.

* cw/worktree-extension:
  worktree: refactor `repair_worktree_after_gitdir_move()`
  worktree: add relative cli/config options to `repair` command
  worktree: add relative cli/config options to `move` command
  worktree: add relative cli/config options to `add` command
  worktree: add `write_worktree_linking_files()` function
  worktree: refactor infer_backlink return
  worktree: add `relativeWorktrees` extension
  setup: correctly reinitialize repository version

Documentation/config/extensions.txt

@@ -63,6 +63,12 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1]. Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+relativeWorktrees::
+	If enabled, indicates at least one worktree has been linked with
+	relative paths. Automatically set if a worktree has been created or
+	repaired with either the `--relative-paths` option or with the
+	`worktree.useRelativePaths` config set to `true`.
+
 worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the

Documentation/config/worktree.txt

@@ -7,3 +7,13 @@ worktree.guessRemote::
 	such a branch exists, it is checked out and set as "upstream"
 	for the new branch.  If no such match can be found, it falls
 	back to creating a new branch from the current HEAD.
+
+worktree.useRelativePaths::
+	Link worktrees using relative paths (when "true") or absolute
+	paths (when "false"). This is particularly useful for setups
+	where the repository and worktrees may be moved between
+	different locations or environments. Defaults to "false".
++
+Note that setting `worktree.useRelativePaths` to "true" implies enabling the
+`extension.relativeWorktrees` config (see linkgit:git-config[1]),
+thus making it incompatible with older versions of Git.

Documentation/git-worktree.txt

@@ -216,6 +216,14 @@ To remove a locked worktree, specify `--force` twice.
 This can also be set up as the default behaviour by using the
 `worktree.guessRemote` config option.
 
+--[no-]relative-paths::
+	Link worktrees using relative paths or absolute paths (default).
+	Overrides the `worktree.useRelativePaths` config option, see
+	linkgit:git-config[1].
++
+With `repair`, the linking files will be updated if there's an absolute/relative
+mismatch, even if the links are correct.
+
 --[no-]track::
 	When creating a new branch, if `<commit-ish>` is a branch,
 	mark it as "upstream" from the new branch.  This is the

builtin/worktree.c

@@ -120,12 +120,14 @@ struct add_opts {
 	int quiet;
 	int checkout;
 	int orphan;
+	int relative_paths;
 	const char *keep_locked;
 };
 
 static int show_only;
 static int verbose;
 static int guess_remote;
+static int use_relative_paths;
 static timestamp_t expire;
 
 static int git_worktree_config(const char *var, const char *value,
@@ -134,6 +136,9 @@ static int git_worktree_config(const char *var, const char *value,
 	if (!strcmp(var, "worktree.guessremote")) {
 		guess_remote = git_config_bool(var, value);
 		return 0;
+	} else if (!strcmp(var, "worktree.userelativepaths")) {
+		use_relative_paths = git_config_bool(var, value);
+		return 0;
 	}
 
 	return git_default_config(var, value, ctx, cb);
@@ -415,8 +420,7 @@ static int add_worktree(const char *path, const char *refname,
 			const struct add_opts *opts)
 {
 	struct strbuf sb_git = STRBUF_INIT, sb_repo = STRBUF_INIT;
-	struct strbuf sb = STRBUF_INIT, sb_tmp = STRBUF_INIT;
+	struct strbuf sb = STRBUF_INIT;
-	struct strbuf sb_path_realpath = STRBUF_INIT, sb_repo_realpath = STRBUF_INIT;
 	const char *name;
 	struct strvec child_env = STRVEC_INIT;
 	unsigned int counter = 0;
@@ -492,10 +496,7 @@ static int add_worktree(const char *path, const char *refname,
 
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/gitdir", sb_repo.buf);
-	strbuf_realpath(&sb_path_realpath, path, 1);
+	write_worktree_linking_files(sb_git, sb, opts->relative_paths);
-	strbuf_realpath(&sb_repo_realpath, sb_repo.buf, 1);
-	write_file(sb.buf, "%s/.git", relative_path(sb_path_realpath.buf, sb_repo_realpath.buf, &sb_tmp));
-	write_file(sb_git.buf, "gitdir: %s", relative_path(sb_repo_realpath.buf, sb_path_realpath.buf, &sb_tmp));
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
 	write_file(sb.buf, "../..");
@@ -579,12 +580,9 @@ done:
 
 	strvec_clear(&child_env);
 	strbuf_release(&sb);
-	strbuf_release(&sb_tmp);
 	strbuf_release(&symref);
 	strbuf_release(&sb_repo);
-	strbuf_release(&sb_repo_realpath);
 	strbuf_release(&sb_git);
-	strbuf_release(&sb_path_realpath);
 	strbuf_release(&sb_name);
 	free_worktree(wt);
 	return ret;
@@ -798,12 +796,15 @@ static int add(int ac, const char **av, const char *prefix,
 			     PARSE_OPT_NOARG | PARSE_OPT_OPTARG),
 		OPT_BOOL(0, "guess-remote", &guess_remote,
 			 N_("try to match the new branch name with a remote-tracking branch")),
+		OPT_BOOL(0, "relative-paths", &opts.relative_paths,
+			 N_("use relative paths for worktrees")),
 		OPT_END()
 	};
 	int ret;
 
 	memset(&opts, 0, sizeof(opts));
 	opts.checkout = 1;
+	opts.relative_paths = use_relative_paths;
 	ac = parse_options(ac, av, prefix, options, git_worktree_add_usage, 0);
 	if (!!opts.detach + !!new_branch + !!new_branch_force > 1)
 		die(_("options '%s', '%s', and '%s' cannot be used together"), "-b", "-B", "--detach");
@@ -1195,6 +1196,8 @@ static int move_worktree(int ac, const char **av, const char *prefix,
 		OPT__FORCE(&force,
 			 N_("force move even if worktree is dirty or locked"),
 			 PARSE_OPT_NOCOMPLETE),
+		OPT_BOOL(0, "relative-paths", &use_relative_paths,
+			 N_("use relative paths for worktrees")),
 		OPT_END()
 	};
 	struct worktree **worktrees, *wt;
@@ -1247,7 +1250,7 @@ static int move_worktree(int ac, const char **av, const char *prefix,
 	if (rename(wt->path, dst.buf) == -1)
 		die_errno(_("failed to move '%s' to '%s'"), wt->path, dst.buf);
 
-	update_worktree_location(wt, dst.buf);
+	update_worktree_location(wt, dst.buf, use_relative_paths);
 
 	strbuf_release(&dst);
 	free_worktrees(worktrees);
@@ -1390,6 +1393,8 @@ static int repair(int ac, const char **av, const char *prefix,
 	const char **p;
 	const char *self[] = { ".", NULL };
 	struct option options[] = {
+		OPT_BOOL(0, "relative-paths", &use_relative_paths,
+			 N_("use relative paths for worktrees")),
 		OPT_END()
 	};
 	int rc = 0;
@@ -1397,8 +1402,8 @@ static int repair(int ac, const char **av, const char *prefix,
 	ac = parse_options(ac, av, prefix, options, git_worktree_repair_usage, 0);
 	p = ac > 0 ? av : self;
 	for (; *p; p++)
-		repair_worktree_at_path(*p, report_repair, &rc);
+		repair_worktree_at_path(*p, report_repair, &rc, use_relative_paths);
-	repair_worktrees(report_repair, &rc);
+	repair_worktrees(report_repair, &rc, use_relative_paths);
 	return rc;
 }
 

repository.c

@@ -283,6 +283,7 @@ int repo_init(struct repository *repo,
 	repo_set_compat_hash_algo(repo, format.compat_hash_algo);
 	repo_set_ref_storage_format(repo, format.ref_storage_format);
 	repo->repository_format_worktree_config = format.worktree_config;
+	repo->repository_format_relative_worktrees = format.relative_worktrees;
 
 	/* take ownership of format.partial_clone */
 	repo->repository_format_partial_clone = format.partial_clone;

repository.h

@@ -150,6 +150,7 @@ struct repository {
 
 	/* Configurations */
 	int repository_format_worktree_config;
+	int repository_format_relative_worktrees;
 
 	/* Indicate if a repository has a different 'commondir' from 'gitdir' */
 	unsigned different_commondir:1;

setup.c

@@ -683,6 +683,9 @@ static enum extension_result handle_extension(const char *var,
 				     "extensions.refstorage", value);
 		data->ref_storage_format = format;
 		return EXTENSION_OK;
+	} else if (!strcmp(ext, "relativeworktrees")) {
+		data->relative_worktrees = git_config_bool(var, value);
+		return EXTENSION_OK;
 	}
 	return EXTENSION_UNKNOWN;
 }
@@ -1854,6 +1857,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 						    repo_fmt.ref_storage_format);
 			the_repository->repository_format_worktree_config =
 				repo_fmt.worktree_config;
+			the_repository->repository_format_relative_worktrees =
+				repo_fmt.relative_worktrees;
 			/* take ownership of repo_fmt.partial_clone */
 			the_repository->repository_format_partial_clone =
 				repo_fmt.partial_clone;
@@ -1950,6 +1955,8 @@ void check_repository_format(struct repository_format *fmt)
 				    fmt->ref_storage_format);
 	the_repository->repository_format_worktree_config =
 		fmt->worktree_config;
+	the_repository->repository_format_relative_worktrees =
+		fmt->relative_worktrees;
 	the_repository->repository_format_partial_clone =
 		xstrdup_or_null(fmt->partial_clone);
 	clear_repository_format(&repo_fmt);
@@ -2204,8 +2211,8 @@ void initialize_repository_version(int hash_algo,
 				   enum ref_storage_format ref_storage_format,
 				   int reinit)
 {
-	char repo_version_string[10];
+	struct strbuf repo_version = STRBUF_INIT;
-	int repo_version = GIT_REPO_VERSION;
+	int target_version = GIT_REPO_VERSION;
 
 	/*
 	 * Note that we initialize the repository version to 1 when the ref
@@ -2216,12 +2223,7 @@ void initialize_repository_version(int hash_algo,
 	 */
 	if (hash_algo != GIT_HASH_SHA1 ||
 	    ref_storage_format != REF_STORAGE_FORMAT_FILES)
-		repo_version = GIT_REPO_VERSION_READ;
+		target_version = GIT_REPO_VERSION_READ;
-
-	/* This forces creation of new config file */
-	xsnprintf(repo_version_string, sizeof(repo_version_string),
-		  "%d", repo_version);
-	git_config_set("core.repositoryformatversion", repo_version_string);
 
 	if (hash_algo != GIT_HASH_SHA1 && hash_algo != GIT_HASH_UNKNOWN)
 		git_config_set("extensions.objectformat",
@@ -2234,6 +2236,25 @@ void initialize_repository_version(int hash_algo,
 			       ref_storage_format_to_name(ref_storage_format));
 	else if (reinit)
 		git_config_set_gently("extensions.refstorage", NULL);
+
+	if (reinit) {
+		struct strbuf config = STRBUF_INIT;
+		struct repository_format repo_fmt = REPOSITORY_FORMAT_INIT;
+
+		strbuf_git_common_path(&config, the_repository, "config");
+		read_repository_format(&repo_fmt, config.buf);
+
+		if (repo_fmt.v1_only_extensions.nr)
+			target_version = GIT_REPO_VERSION_READ;
+
+		strbuf_release(&config);
+		clear_repository_format(&repo_fmt);
+	}
+
+	strbuf_addf(&repo_version, "%d", target_version);
+	git_config_set("core.repositoryformatversion", repo_version.buf);
+
+	strbuf_release(&repo_version);
 }
 
 static int is_reinit(void)
@@ -2333,7 +2354,7 @@ static int create_default_files(const char *template_path,
 		adjust_shared_perm(repo_get_git_dir(the_repository));
 	}
 
-	initialize_repository_version(fmt->hash_algo, fmt->ref_storage_format, 0);
+	initialize_repository_version(fmt->hash_algo, fmt->ref_storage_format, reinit);
 
 	/* Check filemode trustability */
 	path = git_path_buf(&buf, "config");

setup.h

@@ -129,6 +129,7 @@ struct repository_format {
 	int precious_objects;
 	char *partial_clone; /* value of extensions.partialclone */
 	int worktree_config;
+	int relative_worktrees;
 	int is_bare;
 	int hash_algo;
 	int compat_hash_algo;

t/t0001-init.sh

@@ -433,6 +433,12 @@ test_expect_success SYMLINKS 're-init to move gitdir symlink' '
 sep_git_dir_worktree ()  {
 	test_when_finished "rm -rf mainwt linkwt seprepo" &&
 	git init mainwt &&
+	if test "relative" = $2
+	then
+		test_config -C mainwt worktree.useRelativePaths true
+	else
+		test_config -C mainwt worktree.useRelativePaths false
+	fi
 	test_commit -C mainwt gumby &&
 	git -C mainwt worktree add --detach ../linkwt &&
 	git -C "$1" init --separate-git-dir ../seprepo &&
@@ -441,12 +447,20 @@ sep_git_dir_worktree ()  {
 	test_cmp expect actual
 }
 
-test_expect_success 're-init to move gitdir with linked worktrees' '
+test_expect_success 're-init to move gitdir with linked worktrees (absolute)' '
-	sep_git_dir_worktree mainwt
+	sep_git_dir_worktree mainwt absolute
 '
 
-test_expect_success 're-init to move gitdir within linked worktree' '
+test_expect_success 're-init to move gitdir within linked worktree (absolute)' '
-	sep_git_dir_worktree linkwt
+	sep_git_dir_worktree linkwt absolute
+'
+
+test_expect_success 're-init to move gitdir with linked worktrees (relative)' '
+	sep_git_dir_worktree mainwt relative
+'
+
+test_expect_success 're-init to move gitdir within linked worktree (relative)' '
+	sep_git_dir_worktree linkwt relative
 '
 
 test_expect_success MINGW '.git hidden' '

t/t2400-worktree-add.sh

@@ -1206,4 +1206,50 @@ test_expect_success '"add" with initialized submodule, with submodule.recurse se
 	git -C project-clone -c submodule.recurse worktree add ../project-5
 '
 
+test_expect_success 'can create worktrees with relative paths' '
+	test_when_finished "git worktree remove relative" &&
+	test_config worktree.useRelativePaths false &&
+	git worktree add --relative-paths ./relative &&
+	echo "gitdir: ../.git/worktrees/relative" >expect &&
+	test_cmp expect relative/.git &&
+	echo "../../../relative/.git" >expect &&
+	test_cmp expect .git/worktrees/relative/gitdir
+'
+
+test_expect_success 'can create worktrees with absolute paths' '
+	test_config worktree.useRelativePaths true &&
+	git worktree add ./relative &&
+	echo "gitdir: ../.git/worktrees/relative" >expect &&
+	test_cmp expect relative/.git &&
+	git worktree add --no-relative-paths ./absolute &&
+	echo "gitdir: $(pwd)/.git/worktrees/absolute" >expect &&
+	test_cmp expect absolute/.git &&
+	echo "$(pwd)/absolute/.git" >expect &&
+	test_cmp expect .git/worktrees/absolute/gitdir
+'
+
+test_expect_success 'move repo without breaking relative internal links' '
+	test_when_finished rm -rf repo moved &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit initial &&
+		git worktree add --relative-paths wt1 &&
+		cd .. &&
+		mv repo moved &&
+		cd moved/wt1 &&
+		git worktree list >out 2>err &&
+		test_must_be_empty err
+	)
+'
+
+test_expect_success 'relative worktree sets extension config' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	git -C repo commit --allow-empty -m base &&
+	git -C repo worktree add --relative-paths ./foo &&
+	test_cmp_config -C repo 1 core.repositoryformatversion &&
+	test_cmp_config -C repo true extensions.relativeworktrees
+'
+
 test_done

t/t2401-worktree-prune.sh

@@ -119,11 +119,12 @@ test_expect_success 'prune duplicate (main/linked)' '
 	! test -d .git/worktrees/wt
 '
 
-test_expect_success 'not prune proper worktrees when run inside linked worktree' '
+test_expect_success 'not prune proper worktrees inside linked worktree with relative paths' '
 	test_when_finished rm -rf repo wt_ext &&
 	git init repo &&
 	(
 	    cd repo &&
+	    git config worktree.useRelativePaths true &&
 	    echo content >file &&
 	    git add file &&
 	    git commit -m msg &&

t/t2402-worktree-list.sh

@@ -260,6 +260,7 @@ test_expect_success 'broken main worktree still at the top' '
 '
 
 test_expect_success 'linked worktrees are sorted' '
+	test_when_finished "rm -rf sorted" &&
 	mkdir sorted &&
 	git init sorted/main &&
 	(
@@ -279,6 +280,27 @@ test_expect_success 'linked worktrees are sorted' '
 	test_cmp expected sorted/main/actual
 '
 
+test_expect_success 'linked worktrees with relative paths are shown with absolute paths' '
+	test_when_finished "rm -rf sorted" &&
+	mkdir sorted &&
+	git init sorted/main &&
+	(
+		cd sorted/main &&
+		test_tick &&
+		test_commit new &&
+		git worktree add --relative-paths ../first &&
+		git worktree add ../second &&
+		git worktree list --porcelain >out &&
+		grep ^worktree out >actual
+	) &&
+	cat >expected <<-EOF &&
+	worktree $(pwd)/sorted/main
+	worktree $(pwd)/sorted/first
+	worktree $(pwd)/sorted/second
+	EOF
+	test_cmp expected sorted/main/actual
+'
+
 test_expect_success 'worktree path when called in .git directory' '
 	git worktree list >list1 &&
 	git -C .git worktree list >list2 &&

t/t2403-worktree-move.sh

@@ -246,4 +246,29 @@ test_expect_success 'not remove a repo with initialized submodule' '
 	)
 '
 
+test_expect_success 'move worktree with absolute path to relative path' '
+	test_config worktree.useRelativePaths false &&
+	git worktree add ./absolute &&
+	git worktree move --relative-paths absolute relative &&
+	echo "gitdir: ../.git/worktrees/absolute" >expect &&
+	test_cmp expect relative/.git &&
+	echo "../../../relative/.git" >expect &&
+	test_cmp expect .git/worktrees/absolute/gitdir &&
+	test_config worktree.useRelativePaths true &&
+	git worktree move relative relative2 &&
+	echo "gitdir: ../.git/worktrees/absolute" >expect &&
+	test_cmp expect relative2/.git &&
+	echo "../../../relative2/.git" >expect &&
+	test_cmp expect .git/worktrees/absolute/gitdir
+'
+
+test_expect_success 'move worktree with relative path to absolute path' '
+	test_config worktree.useRelativePaths true &&
+	git worktree move --no-relative-paths relative2 absolute &&
+	echo "gitdir: $(pwd)/.git/worktrees/absolute" >expect &&
+	test_cmp expect absolute/.git &&
+	echo "$(pwd)/absolute/.git" >expect &&
+	test_cmp expect .git/worktrees/absolute/gitdir
+'
+
 test_done

t/t2406-worktree-repair.sh

@@ -215,4 +215,43 @@ test_expect_success 'repair copied main and linked worktrees' '
 	test_cmp dup/linked.expect dup/linked/.git
 '
 
+test_expect_success 'repair worktree with relative path with missing gitfile' '
+	test_when_finished "rm -rf main wt" &&
+	test_create_repo main &&
+	git -C main config worktree.useRelativePaths true &&
+	test_commit -C main init &&
+	git -C main worktree add --detach ../wt &&
+	rm wt/.git &&
+	test_path_is_missing wt/.git &&
+	git -C main worktree repair &&
+	echo "gitdir: ../main/.git/worktrees/wt" >expect &&
+	test_cmp expect wt/.git
+'
+
+test_expect_success 'repair absolute worktree to use relative paths' '
+	test_when_finished "rm -rf main side sidemoved" &&
+	test_create_repo main &&
+	test_commit -C main init &&
+	git -C main worktree add --detach ../side &&
+	echo "../../../../sidemoved/.git" >expect-gitdir &&
+	echo "gitdir: ../main/.git/worktrees/side" >expect-gitfile &&
+	mv side sidemoved &&
+	git -C main worktree repair --relative-paths ../sidemoved &&
+	test_cmp expect-gitdir main/.git/worktrees/side/gitdir &&
+	test_cmp expect-gitfile sidemoved/.git
+'
+
+test_expect_success 'repair relative worktree to use absolute paths' '
+	test_when_finished "rm -rf main side sidemoved" &&
+	test_create_repo main &&
+	test_commit -C main init &&
+	git -C main worktree add --relative-paths --detach ../side &&
+	echo "$(pwd)/sidemoved/.git" >expect-gitdir &&
+	echo "gitdir: $(pwd)/main/.git/worktrees/side" >expect-gitfile &&
+	mv side sidemoved &&
+	git -C main worktree repair ../sidemoved &&
+	test_cmp expect-gitdir main/.git/worktrees/side/gitdir &&
+	test_cmp expect-gitfile sidemoved/.git
+'
+
 test_done

t/t2408-worktree-relative.sh

@@ -1,38 +0,0 @@
-#!/bin/sh
-
-test_description='test worktrees linked with relative paths'
-
-. ./test-lib.sh
-
-test_expect_success 'links worktrees with relative paths' '
-	test_when_finished rm -rf repo &&
-	git init repo &&
-	(
-		cd repo &&
-		test_commit initial &&
-		git worktree add wt1 &&
-		echo "../../../wt1/.git" >expected_gitdir &&
-		cat .git/worktrees/wt1/gitdir >actual_gitdir &&
-		echo "gitdir: ../.git/worktrees/wt1" >expected_git &&
-		cat wt1/.git >actual_git &&
-		test_cmp expected_gitdir actual_gitdir &&
-		test_cmp expected_git actual_git
-	)
-'
-
-test_expect_success 'move repo without breaking relative internal links' '
-	test_when_finished rm -rf repo moved &&
-	git init repo &&
-	(
-		cd repo &&
-		test_commit initial &&
-		git worktree add wt1 &&
-		cd .. &&
-		mv repo moved &&
-		cd moved/wt1 &&
-		git status >out 2>err &&
-		test_must_be_empty err
-	)
-'
-
-test_done

t/t5504-fetch-receive-strict.sh

@@ -170,7 +170,7 @@ test_expect_success 'fsck with invalid or bogus skipList input' '
 	test_must_fail git -c fsck.skipList=does-not-exist -c fsck.missingEmail=ignore fsck 2>err &&
 	test_grep "could not open.*: does-not-exist" err &&
 	test_must_fail git -c fsck.skipList=.git/config -c fsck.missingEmail=ignore fsck 2>err &&
-	test_grep "invalid object name: \[core\]" err
+	test_grep "invalid object name: " err
 '
 
 test_expect_success 'fsck with other accepted skipList input (comments & empty lines)' '
@@ -233,7 +233,7 @@ test_expect_success 'push with receive.fsck.skipList' '
 	test_grep "could not open.*: does-not-exist" err &&
 	git --git-dir=dst/.git config receive.fsck.skipList config &&
 	test_must_fail git push --porcelain dst bogus 2>err &&
-	test_grep "invalid object name: \[core\]" err &&
+	test_grep "invalid object name: " err &&
 
 	git --git-dir=dst/.git config receive.fsck.skipList SKIP &&
 	git push --porcelain dst bogus
@@ -262,7 +262,7 @@ test_expect_success 'fetch with fetch.fsck.skipList' '
 	test_grep "could not open.*: does-not-exist" err &&
 	git --git-dir=dst/.git config fetch.fsck.skipList dst/.git/config &&
 	test_must_fail git --git-dir=dst/.git fetch "file://$(pwd)" $refspec 2>err &&
-	test_grep "invalid object name: \[core\]" err &&
+	test_grep "invalid object name: " err &&
 
 	git --git-dir=dst/.git config fetch.fsck.skipList dst/.git/SKIP &&
 	git --git-dir=dst/.git fetch "file://$(pwd)" $refspec

worktree.c

@@ -111,9 +111,9 @@ struct worktree *get_linked_worktree(const char *id,
 	strbuf_strip_suffix(&worktree_path, "/.git");
 
 	if (!is_absolute_path(worktree_path.buf)) {
-	    strbuf_strip_suffix(&path, "gitdir");
+		strbuf_strip_suffix(&path, "gitdir");
-	    strbuf_addbuf(&path, &worktree_path);
+		strbuf_addbuf(&path, &worktree_path);
-	    strbuf_realpath_forgiving(&worktree_path, path.buf, 0);
+		strbuf_realpath_forgiving(&worktree_path, path.buf, 0);
 	}
 
 	CALLOC_ARRAY(worktree, 1);
@@ -376,32 +376,28 @@ done:
 	return ret;
 }
 
-void update_worktree_location(struct worktree *wt, const char *path_)
+void update_worktree_location(struct worktree *wt, const char *path_,
+			      int use_relative_paths)
 {
 	struct strbuf path = STRBUF_INIT;
-	struct strbuf repo = STRBUF_INIT;
+	struct strbuf dotgit = STRBUF_INIT;
-	struct strbuf file = STRBUF_INIT;
+	struct strbuf gitdir = STRBUF_INIT;
-	struct strbuf tmp = STRBUF_INIT;
 
 	if (is_main_worktree(wt))
 		BUG("can't relocate main worktree");
 
-	strbuf_realpath(&repo, git_common_path("worktrees/%s", wt->id), 1);
+	strbuf_realpath(&gitdir, git_common_path("worktrees/%s/gitdir", wt->id), 1);
 	strbuf_realpath(&path, path_, 1);
+	strbuf_addf(&dotgit, "%s/.git", path.buf);
 	if (fspathcmp(wt->path, path.buf)) {
-		strbuf_addf(&file, "%s/gitdir", repo.buf);
+		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
-		write_file(file.buf, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
-		strbuf_reset(&file);
-		strbuf_addf(&file, "%s/.git", path.buf);
-		write_file(file.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
 
 		free(wt->path);
 		wt->path = strbuf_detach(&path, NULL);
 	}
 	strbuf_release(&path);
-	strbuf_release(&repo);
+	strbuf_release(&dotgit);
-	strbuf_release(&file);
+	strbuf_release(&gitdir);
-	strbuf_release(&tmp);
 }
 
 int is_worktree_being_rebased(const struct worktree *wt,
@@ -577,12 +573,13 @@ int other_head_refs(each_ref_fn fn, void *cb_data)
  * pointing at <repo>/worktrees/<id>.
  */
 static void repair_gitfile(struct worktree *wt,
-			   worktree_repair_fn fn, void *cb_data)
+			   worktree_repair_fn fn, void *cb_data,
+			   int use_relative_paths)
 {
 	struct strbuf dotgit = STRBUF_INIT;
+	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf repo = STRBUF_INIT;
 	struct strbuf backlink = STRBUF_INIT;
-	struct strbuf tmp = STRBUF_INIT;
 	char *dotgit_contents = NULL;
 	const char *repair = NULL;
 	int err;
@@ -598,6 +595,7 @@ static void repair_gitfile(struct worktree *wt,
 
 	strbuf_realpath(&repo, git_common_path("worktrees/%s", wt->id), 1);
 	strbuf_addf(&dotgit, "%s/.git", wt->path);
+	strbuf_addf(&gitdir, "%s/gitdir", repo.buf);
 	dotgit_contents = xstrdup_or_null(read_gitfile_gently(dotgit.buf, &err));
 
 	if (dotgit_contents) {
@@ -615,18 +613,20 @@ static void repair_gitfile(struct worktree *wt,
 		repair = _(".git file broken");
 	else if (fspathcmp(backlink.buf, repo.buf))
 		repair = _(".git file incorrect");
+	else if (use_relative_paths == is_absolute_path(dotgit_contents))
+		repair = _(".git file absolute/relative path mismatch");
 
 	if (repair) {
 		fn(0, wt->path, repair, cb_data);
-		write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, wt->path, &tmp));
+		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
 	}
 
 done:
 	free(dotgit_contents);
 	strbuf_release(&repo);
 	strbuf_release(&dotgit);
+	strbuf_release(&gitdir);
 	strbuf_release(&backlink);
-	strbuf_release(&tmp);
 }
 
 static void repair_noop(int iserr UNUSED,
@@ -637,7 +637,7 @@ static void repair_noop(int iserr UNUSED,
 	/* nothing */
 }
 
-void repair_worktrees(worktree_repair_fn fn, void *cb_data)
+void repair_worktrees(worktree_repair_fn fn, void *cb_data, int use_relative_paths)
 {
 	struct worktree **worktrees = get_worktrees_internal(1);
 	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
@@ -645,51 +645,38 @@ void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 	if (!fn)
 		fn = repair_noop;
 	for (; *wt; wt++)
-		repair_gitfile(*wt, fn, cb_data);
+		repair_gitfile(*wt, fn, cb_data, use_relative_paths);
 	free_worktrees(worktrees);
 }
 
 void repair_worktree_after_gitdir_move(struct worktree *wt, const char *old_path)
 {
-	struct strbuf path = STRBUF_INIT;
-	struct strbuf repo = STRBUF_INIT;
 	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf dotgit = STRBUF_INIT;
-	struct strbuf olddotgit = STRBUF_INIT;
+	int is_relative_path;
-	struct strbuf tmp = STRBUF_INIT;
 
 	if (is_main_worktree(wt))
 		goto done;
 
-	strbuf_realpath(&repo, git_common_path("worktrees/%s", wt->id), 1);
+	strbuf_realpath(&gitdir, git_common_path("worktrees/%s/gitdir", wt->id), 1);
-	strbuf_addf(&gitdir, "%s/gitdir", repo.buf);
 
-	if (strbuf_read_file(&olddotgit, gitdir.buf, 0) < 0)
+	if (strbuf_read_file(&dotgit, gitdir.buf, 0) < 0)
 		goto done;
 
-	strbuf_rtrim(&olddotgit);
+	strbuf_rtrim(&dotgit);
-	if (is_absolute_path(olddotgit.buf)) {
+	is_relative_path = ! is_absolute_path(dotgit.buf);
-		strbuf_addbuf(&dotgit, &olddotgit);
+	if (is_relative_path) {
-	} else {
+		strbuf_insertf(&dotgit, 0, "%s/worktrees/%s/", old_path, wt->id);
-		strbuf_addf(&dotgit, "%s/worktrees/%s/%s", old_path, wt->id, olddotgit.buf);
 		strbuf_realpath_forgiving(&dotgit, dotgit.buf, 0);
 	}
 
 	if (!file_exists(dotgit.buf))
 		goto done;
 
-	strbuf_addbuf(&path, &dotgit);
+	write_worktree_linking_files(dotgit, gitdir, is_relative_path);
-	strbuf_strip_suffix(&path, "/.git");
-
-	write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
-	write_file(gitdir.buf, "%s", relative_path(dotgit.buf, repo.buf, &tmp));
 done:
-	strbuf_release(&path);
-	strbuf_release(&repo);
 	strbuf_release(&gitdir);
 	strbuf_release(&dotgit);
-	strbuf_release(&olddotgit);
-	strbuf_release(&tmp);
 }
 
 void repair_worktrees_after_gitdir_move(const char *old_path)
@@ -725,8 +712,10 @@ static int is_main_worktree_path(const char *path)
  * won't know which <repo>/worktrees/<id>/gitdir to repair. However, we may
  * be able to infer the gitdir by manually reading /path/to/worktree/.git,
  * extracting the <id>, and checking if <repo>/worktrees/<id> exists.
+ *
+ * Returns -1 on failure and strbuf.len on success.
  */
-static int infer_backlink(const char *gitfile, struct strbuf *inferred)
+static ssize_t infer_backlink(const char *gitfile, struct strbuf *inferred)
 {
 	struct strbuf actual = STRBUF_INIT;
 	const char *id;
@@ -747,12 +736,11 @@ static int infer_backlink(const char *gitfile, struct strbuf *inferred)
 		goto error;
 
 	strbuf_release(&actual);
-	return 1;
+	return inferred->len;
-
 error:
 	strbuf_release(&actual);
 	strbuf_reset(inferred); /* clear invalid path */
-	return 0;
+	return -1;
 }
 
 /*
@@ -760,16 +748,14 @@ error:
  * the worktree's path.
  */
 void repair_worktree_at_path(const char *path,
-			     worktree_repair_fn fn, void *cb_data)
+			     worktree_repair_fn fn, void *cb_data,
+			     int use_relative_paths)
 {
 	struct strbuf dotgit = STRBUF_INIT;
-	struct strbuf realdotgit = STRBUF_INIT;
 	struct strbuf backlink = STRBUF_INIT;
 	struct strbuf inferred_backlink = STRBUF_INIT;
 	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf olddotgit = STRBUF_INIT;
-	struct strbuf realolddotgit = STRBUF_INIT;
-	struct strbuf tmp = STRBUF_INIT;
 	char *dotgit_contents = NULL;
 	const char *repair = NULL;
 	int err;
@@ -781,25 +767,25 @@ void repair_worktree_at_path(const char *path,
 		goto done;
 
 	strbuf_addf(&dotgit, "%s/.git", path);
-	if (!strbuf_realpath(&realdotgit, dotgit.buf, 0)) {
+	if (!strbuf_realpath(&dotgit, dotgit.buf, 0)) {
 		fn(1, path, _("not a valid path"), cb_data);
 		goto done;
 	}
 
-	infer_backlink(realdotgit.buf, &inferred_backlink);
+	infer_backlink(dotgit.buf, &inferred_backlink);
 	strbuf_realpath_forgiving(&inferred_backlink, inferred_backlink.buf, 0);
-	dotgit_contents = xstrdup_or_null(read_gitfile_gently(realdotgit.buf, &err));
+	dotgit_contents = xstrdup_or_null(read_gitfile_gently(dotgit.buf, &err));
 	if (dotgit_contents) {
 		if (is_absolute_path(dotgit_contents)) {
 			strbuf_addstr(&backlink, dotgit_contents);
 		} else {
-			strbuf_addbuf(&backlink, &realdotgit);
+			strbuf_addbuf(&backlink, &dotgit);
 			strbuf_strip_suffix(&backlink, ".git");
 			strbuf_addstr(&backlink, dotgit_contents);
 			strbuf_realpath_forgiving(&backlink, backlink.buf, 0);
 		}
 	} else if (err == READ_GITFILE_ERR_NOT_A_FILE) {
-		fn(1, realdotgit.buf, _("unable to locate repository; .git is not a file"), cb_data);
+		fn(1, dotgit.buf, _("unable to locate repository; .git is not a file"), cb_data);
 		goto done;
 	} else if (err == READ_GITFILE_ERR_NOT_A_REPO) {
 		if (inferred_backlink.len) {
@@ -812,11 +798,11 @@ void repair_worktree_at_path(const char *path,
 			 */
 			strbuf_swap(&backlink, &inferred_backlink);
 		} else {
-			fn(1, realdotgit.buf, _("unable to locate repository; .git file does not reference a repository"), cb_data);
+			fn(1, dotgit.buf, _("unable to locate repository; .git file does not reference a repository"), cb_data);
 			goto done;
 		}
 	} else {
-		fn(1, realdotgit.buf, _("unable to locate repository; .git file broken"), cb_data);
+		fn(1, dotgit.buf, _("unable to locate repository; .git file broken"), cb_data);
 		goto done;
 	}
 
@@ -838,39 +824,35 @@ void repair_worktree_at_path(const char *path,
 	 * in the "copy" repository. In this case, point the "copy" worktree's
 	 * .git file at the "copy" repository.
 	 */
-	if (inferred_backlink.len && fspathcmp(backlink.buf, inferred_backlink.buf)) {
+	if (inferred_backlink.len && fspathcmp(backlink.buf, inferred_backlink.buf))
 		strbuf_swap(&backlink, &inferred_backlink);
-	}
 
 	strbuf_addf(&gitdir, "%s/gitdir", backlink.buf);
 	if (strbuf_read_file(&olddotgit, gitdir.buf, 0) < 0)
 		repair = _("gitdir unreadable");
+	else if (use_relative_paths == is_absolute_path(olddotgit.buf))
+		repair = _("gitdir absolute/relative path mismatch");
 	else {
 		strbuf_rtrim(&olddotgit);
-		if (is_absolute_path(olddotgit.buf)) {
+		if (!is_absolute_path(olddotgit.buf)) {
-			strbuf_addbuf(&realolddotgit, &olddotgit);
+			strbuf_insertf(&olddotgit, 0, "%s/", backlink.buf);
-		} else {
+			strbuf_realpath_forgiving(&olddotgit, olddotgit.buf, 0);
-			strbuf_addf(&realolddotgit, "%s/%s", backlink.buf, olddotgit.buf);
-			strbuf_realpath_forgiving(&realolddotgit, realolddotgit.buf, 0);
 		}
-		if (fspathcmp(realolddotgit.buf, realdotgit.buf))
+		if (fspathcmp(olddotgit.buf, dotgit.buf))
 			repair = _("gitdir incorrect");
 	}
 
 	if (repair) {
 		fn(0, gitdir.buf, repair, cb_data);
-		write_file(gitdir.buf, "%s", relative_path(realdotgit.buf, backlink.buf, &tmp));
+		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
 	}
 done:
 	free(dotgit_contents);
 	strbuf_release(&olddotgit);
-	strbuf_release(&realolddotgit);
 	strbuf_release(&backlink);
 	strbuf_release(&inferred_backlink);
 	strbuf_release(&gitdir);
-	strbuf_release(&realdotgit);
 	strbuf_release(&dotgit);
-	strbuf_release(&tmp);
 }
 
 int should_prune_worktree(const char *id, struct strbuf *reason, char **wtpath, timestamp_t expire)
@@ -1031,3 +1013,38 @@ cleanup:
 	free(main_worktree_file);
 	return res;
 }
+
+void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
+				  int use_relative_paths)
+{
+	struct strbuf path = STRBUF_INIT;
+	struct strbuf repo = STRBUF_INIT;
+	struct strbuf tmp = STRBUF_INIT;
+
+	strbuf_addbuf(&path, &dotgit);
+	strbuf_strip_suffix(&path, "/.git");
+	strbuf_realpath(&path, path.buf, 1);
+	strbuf_addbuf(&repo, &gitdir);
+	strbuf_strip_suffix(&repo, "/gitdir");
+	strbuf_realpath(&repo, repo.buf, 1);
+
+	if (use_relative_paths && !the_repository->repository_format_relative_worktrees) {
+		if (upgrade_repository_format(1) < 0)
+			die(_("unable to upgrade repository format to support relative worktrees"));
+		if (git_config_set_gently("extensions.relativeWorktrees", "true"))
+			die(_("unable to set extensions.relativeWorktrees setting"));
+		the_repository->repository_format_relative_worktrees = 1;
+	}
+
+	if (use_relative_paths) {
+		write_file(gitdir.buf, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
+		write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
+	} else {
+		write_file(gitdir.buf, "%s/.git", path.buf);
+		write_file(dotgit.buf, "gitdir: %s", repo.buf);
+	}
+
+	strbuf_release(&path);
+	strbuf_release(&repo);
+	strbuf_release(&tmp);
+}

worktree.h

@@ -117,8 +117,8 @@ int validate_worktree(const struct worktree *wt,
 /*
  * Update worktrees/xxx/gitdir with the new path.
  */
-void update_worktree_location(struct worktree *wt,
+void update_worktree_location(struct worktree *wt, const char *path_,
-			      const char *path_);
+			      int use_relative_paths);
 
 typedef void (* worktree_repair_fn)(int iserr, const char *path,
 				    const char *msg, void *cb_data);
@@ -129,7 +129,7 @@ typedef void (* worktree_repair_fn)(int iserr, const char *path,
  * function, if non-NULL, is called with the path of the worktree and a
  * description of the repair or error, along with the callback user-data.
  */
-void repair_worktrees(worktree_repair_fn, void *cb_data);
+void repair_worktrees(worktree_repair_fn, void *cb_data, int use_relative_paths);
 
 /*
  * Repair the linked worktrees after the gitdir has been moved.
@@ -151,7 +151,8 @@ void repair_worktree_after_gitdir_move(struct worktree *wt, const char *old_path
  * worktree and a description of the repair or error, along with the callback
  * user-data.
  */
-void repair_worktree_at_path(const char *, worktree_repair_fn, void *cb_data);
+void repair_worktree_at_path(const char *, worktree_repair_fn,
+			     void *cb_data, int use_relative_paths);
 
 /*
  * Free up the memory for a worktree.
@@ -215,4 +216,17 @@ void strbuf_worktree_ref(const struct worktree *wt,
  */
 int init_worktree_config(struct repository *r);
 
+/**
+ * Write the .git file and gitdir file that links the worktree to the repository.
+ *
+ * The `dotgit` parameter is the path to the worktree's .git file, and `gitdir`
+ * is the path to the repository's `gitdir` file.
+ *
+ * Example
+ *  dotgit: "/path/to/foo/.git"
+ *  gitdir: "/path/to/repo/worktrees/foo/gitdir"
+ */
+void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
+				  int use_relative_paths);
+
 #endif